Catalysts comprising metals and metal compounds dispersed on a porous support material have been well known and used in the chemicals industry for many years, for a variety of purposes including hydrogenation, dehydrogenation of chemical feedstocks. U.S. Pat. No. 4,490,480 describes such catalysts, useful for various hydrogenation reactions, which consist of 5 to 40% (w/w) of nickel upon a transition alumina, in particular gamma alumina support. These catalysts have an active nickel surface area of between 80 and 300, preferably 100-250 m2/g of nickel and the nickel crystallites have an average diameter of 1 to 5, preferably 1.5 to 3 nm. The nickel crystallites are dispersed for at least 95% in the pores of the alumina. The patent describes a method of making catalysts by heating an aqueous suspension or mixture of a transition alumina in a dissolved nickel ammine complex for some time to a temperature of 60-100° C., preferably 75-95° C., which causes the precipitation of nickel hydroxide. The catalyst suspension is separated off and, if desired, washed, thereafter dried and calcined to nickel oxide and, if need be, reduced. Alternatively, alumina pellets or extrudates are impregnated with a concentrated solution of a nickel ammine complex; subsequently nickel is precipitated by temperature increase.
U.S. Pat. No. 4,920,089 provides a nickel upon transition alumina catalyst containing 5-40% w/w of nickel, with an active nickel surface area between 80 and 300 m2/g of Ni, with a transition alumina that satisfies a particular X-ray diffraction pattern. Preferably, the BET total surface area of the catalyst is between 50 and 200 m2/g catalyst and is substantially free from pores with a radius below 2.0 nm. The catalysts were prepared by impregnating shaped theta-alumina particles with an ammoniacal nickel solution having a particularly high pH value, namely between 9 and 11, and subsequently evaporating the impregnated alumina particles to dryness, calcining and reducing.
The methods described in the above-mentioned prior art patents enable highly disperse and active metal catalysts to be formed which have been highly successful. We have found, however, that it has not been possible to prepare catalysts in the form of pellets or shaped forms suitable for fixed bed-type reactions which have a metal content greater than about 33% w/w and which have a high metal dispersion coupled with a high crush strength. It is an object of the invention to provide such a catalyst.